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1 /*
2  * Copyright 2017 Timothy Arceri
3  *
4  * Permission is hereby granted, free of charge, to any person obtaining a
5  * copy of this software and associated documentation files (the "Software"),
6  * to deal in the Software without restriction, including without limitation
7  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
8  * and/or sell copies of the Software, and to permit persons to whom the
9  * Software is furnished to do so, subject to the following conditions:
10  *
11  * The above copyright notice and this permission notice (including the next
12  * paragraph) shall be included in all copies or substantial portions of the
13  * Software.
14  *
15  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
16  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
17  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
18  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
19  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
20  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
21  * SOFTWARE.
22  *
23  */
24 
25 #if defined(__linux__)
26 #include <sys/file.h>
27 #include <unistd.h>
28 #include <fcntl.h>
29 #else
30 #include <time.h>
31 #endif
32 
33 #include "rand_xor.h"
34 
35 /* Super fast random number generator.
36  *
37  * This rand_xorshift128plus function by Sebastiano Vigna belongs
38  * to the public domain.
39  */
40 uint64_t
rand_xorshift128plus(uint64_t * seed)41 rand_xorshift128plus(uint64_t *seed)
42 {
43    uint64_t *s = seed;
44 
45    uint64_t s1 = s[0];
46    const uint64_t s0 = s[1];
47    s[0] = s0;
48    s1 ^= s1 << 23;
49    s[1] = s1 ^ s0 ^ (s1 >> 18) ^ (s0 >> 5);
50 
51    return s[1] + s0;
52 }
53 
54 void
s_rand_xorshift128plus(uint64_t * seed,bool randomised_seed)55 s_rand_xorshift128plus(uint64_t *seed, bool randomised_seed)
56 {
57    if (!randomised_seed)
58       goto fixed_seed;
59 
60 #if defined(__linux__)
61    int fd = open("/dev/urandom", O_RDONLY);
62    if (fd < 0)
63       goto fixed_seed;
64 
65    size_t seed_size = sizeof(uint64_t) * 2;
66    if (read(fd, seed, seed_size) != seed_size) {
67       close(fd);
68       goto fixed_seed;
69    }
70 
71    close(fd);
72    return;
73 
74 #else
75    seed[0] = 0x3bffb83978e24f88;
76    seed[1] = time(NULL);
77 
78    return;
79 #endif
80 
81 fixed_seed:
82 
83    /* Fallback to a fixed seed */
84    seed[0] = 0x3bffb83978e24f88;
85    seed[1] = 0x9238d5d56c71cd35;
86 }
87